Cycle does not reflect changes directly
You can use the Solid View for texture painting with some success if you are looking to really examine your painting in context of what you are changing in the specific texture. I set it to Flat and turn off shadows.


You can also use the Material View with blurred background, or turn on full background HDRI and lights from scene if you want to get a better idea of what your painting is doing in its interaction with your shading tree.



I think switching to Cycles render view is better for previewing the effect you have built up and to check your shaders, and not for the actual act of painting. The Material view has a very good result in comparison, and can be used as a preview of what it might look like before switching workflow to the shader tree for tweaking.